Determination of the Level of Mercury Toxicity of Fish in Rivers Draining Gold Panning Sites in the Territory of Fizi, Eastern Democratic Republic of Congo

Abstract

The specimens of the studied fish were taken from the same sites along the rivers during 4 Campaigns (August 2016, December 2016, August 2017 and December 2017). This study specifically aims to evaluate the level of mercury toxicity in fish from these rivers based on their total mercury content and the ratio between the molar concentrations of total selenium and total mercury (TSe: THg). Total selenium and total mercury were measured in fish by atomic absorption spectrophotometry (AAS). The molar concentrations of total mercury were determined by dividing the total mercury concentrations obtained for each fish by its molar mass of about 200.59 g.mol-1. Also, the total selenium molar concentrations were determined by dividing the total selenium contents obtained for each fish by its molar mass of order of 78.9 g.mol-1. In addition, the ratios between the molar concentrations of total selenium and total mercury (TSe: THg) were calculated from the quotient between the molar concentrations of total selenium and total mercury. The results found that all fish from the rivers of the Fizi gold panning sites studied had total mercury concentrations well above the fish quality standards (0.5 mg.Kg-1). Silurus sp fish had the highest total mercury levels compared to other fish, followed respectively by Haplochromis sp and Oreochromis sp. However, it was found that all these species of fish studied do not pose a threat to human health because their molar concentrations of total selenium and total mercury (TSe: THg) are at least greater than 1. Oreochromis sp had the highest ratios of TSe: THg molar concentrations to other fish successively followed by fish Haplochromis sp and Silurus sp. It would be necessary to train gold miners in the territory of Fizi about the proper management of gold washing effluents.